1. Field of the Invention
The present invention relates to an optical lens system of a mobile camera. In the optical system of the mobile camera, optical beams incident at the divided view angles are incident on off-axis lenses arranged at the center portion of an optical lens, and image sensors are separately arranged on both sides of the optical lens. Due to the adjacent arrangement of the off-axis lenses, the disparity of the images can be minimized.
2. Description of the Related Art
With the recent development of mobile terminals such as portable phones and personal digital assistants (PDAs), the mobile terminals provide a phone call function and are used as a multi-convergence device having various functions. The most representative of the multi-convergence is a camera module. The resolution of the camera module changes from 300,000 pixels (VGA) to 700,000 pixels. Moreover, the camera module provides various additional functions, such as auto-focusing (AF) and optical zoom.
Generally, compact camera modules (CCMs) are applied to various IT devices, such as camera phones, smart phones, mobile communication terminals, and toy cameras. Recently, products using the CCMs to meet consumers' various tastes are increasingly put on the market.
The camera modules are manufactured using main parts of charge coupled device (CCD) or complementary metal oxide semiconductor (CMOS) image sensors and lenses. Incident light transmitted through the lens is condensed by the image sensor and is stored as data in the memory. The stored data is displayed as an image through a display medium, such as liquid crystal display (LCD) or PC monitor.
Recently, with the development of digital technologies, the improvement of image compression/decompression technologies, and the technical improvement of peripheral devices of multimedia products, lenses for the mobile cameras have been continuously developed and researched for slim profile and miniaturization. To cope with these trends, mobile cameras are required which have the improved performance and the improved portability, as optical systems for ultraslim camera lenses are included therein.
According to the related art, coaxial lenses are widely used as the optical lenses of mobile cameras. In such a conventional coaxial lens, a plurality of rotationally symmetrical lenses are arranged in a longitudinal direction with respect to an optical axis. Therefore, there is a limitation in reducing the thickness of the longitudinally arranged lenses in the optical axis. Specifically, it is very difficult to achieve the miniaturization of the digital mobile devices because the whole length of the image sensor is determined at a level that is almost equal to the diagonal length of the image sensor.
To solve these problems, an optical lens system using prism lens and an optical lens system using a relay-type off-axis image forming lens have been proposed to achieve the miniaturization of the mobile device. An optical lens using a prism lens and an improved optical lens system using a divided off-axis lens system are disclosed in Korean Patent Application No. 10-2005-0073384, filed by the present applicant. Hereinafter, the optical lens and the improved optical lens system will be described with reference to FIGS. 1 and 2.
Referring to FIG. 1, the optical lens system using the prism lens includes a first prism 10, a second prism 20, a low pass filter (LPF) 4, and an image plane 3, thereby constituting an optical system of a mobile camera. A ratio of a whole length of the optical system to a diagonal length of an image sensor is in a range from 2.4 to 4.3. Therefore, the entire length of the optical system can be reduced within a very limited range.
As another example of the related art, the optical lens system using the off-axis image forming lens of FIG. 2 includes a first plane R1, a second plane R2, a third plane R3, a fourth plane R4, a fifth plane R5, and a sixth plane R6. Specifically, the first plane R1 is an aperture, the second plane R2 is a refraction plane on a coaxis with respect to the first plane R1, and the third plane R3 is a reflection plane inclined with respect to the second plane R2. The fourth plane R4 and the fifth plane R5 are reflection planes that are shifted and inclined with respect to the respective front surfaces. The sixth plane R6 is a refraction plane that is shifted and inclined with respect to the fifth plane R5.
In the integrated off-axis image forming lens system, however, the ratio of the whole length of the lens system to the diagonal length of the image sensor is in the range from 2.4 to 4.3. Therefore, there is a great limitation in securing a wide view angle in a single image sensor and reducing the entire thickness of the optical system.
Accordingly, in order to implement a wide angle of view and reduce the whole length of the optical system for the mobile camera, an additional optical lens system, as well as the lens system using the prism or the integrated off-axis image forming lens system, has to be implemented. An optical lens system using two or more off-axis lens systems is disclosed in Korean Patent Application filed on Aug. 10, 2005 by the present applicant. This optical lens system will be described in brief with reference to FIGS. 3 and 4.
FIG. 3 is a perspective view of an optical lens system according to the related art, and FIG. 4 is a sectional view of the optical lens system illustrated in FIG. 3. In the conventional optical lens system, the view angle is equally divided into more than two angles. The optical lens system includes a plurality of off-axis lens systems 100 and a single image sensor 120. The plurality of off-axis lens systems includes lenses provided on both sides, which transmit optical beams incident at the divided view angles. The single image sensor 120 receives the optical beams transmitted through the plurality of lens systems.
The single image sensor 120 includes unit pixels each receiving one of blue (B), red (R) and green (G) colors. The unit pixels are arranged alternately and regularly.
In the optical lens system, the image sensor 120 is disposed at the center portion of the optical lens having one pair of off-axis lens systems 100 symmetrically arranged on both sides. Therefore, the incident surfaces of the off-axis lens systems 100 have to be arranged on both sides. Consequently, as the distance of the incident surfaces becomes far, the disparity of the images according to the distance of the object occurs.
That is, when the perspective image as illustrated in FIG. 5 is captured, the distortion of the images occurs in the background indicated by a reference symbol “A” in the combination of the images formed through the off-axis lens system 100.